Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$28.61	8.239%	$30.9672	$30.97	$30.95	$31.00
Purchase #2	$98.86	5.524%	$104.321	$104.32	$104.30	$104.30
Purchase #3	$176.48	13.699%	$200.656	$200.66	$200.65	$200.70
Purchase #4	$211.83	5.139%	$222.7159	$222.72	$222.70	$222.70
Purchase #5	$188.27	4.531%	$196.8005	$196.80	$196.80	$196.80
Purchase #6	$230.78	4.525%	$241.2228	$241.22	$241.20	$241.20
Purchase #7	$161.38	11.553%	$180.0242	$180.02	$180.00	$180.00
7 purchase totals =	$1,096.21		$1,176.7076	$1,176.71	$1,176.60	$1,176.70